This application relates to magnetic disc drives and more particularly to an improved hard disc drive spindle motor that minimizes acoustic noise generated by during idle operation of the disc drive.
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator for movement of the heads relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g. a magneto resistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment.
A number of factors determine the speed at which data can be stored and read from the discs. These factors include the density of the data tracks on the discs as well as the speed of the radial actuator. A further significant factor in determining the speed of reading and writing data is the speed of the spindle motor itself which determines the rotational speed of the discs. Specifically, disc rotation speed is highly determinative of the time it takes the radial actuator to access a desired track. It is thus desirable in the disc drive art to have high disc rotation speeds in order to reduce track access times. However, increases in disc drive spindle motor speeds lead to increases in both vibration and acoustic noise levels of the entire disc drive.
A spindle motor typically includes a stator, a rotor and a spindle or shaft. The rotor may alternatively rotate with the shaft or the shaft may be stationary so that the rotor rotates about the shaft. Within a disc drive, the rotor includes a hub for supporting one or more of the rigid, magnetic discs. During idle periods (when the disc drive is neither reading nor writing data to the disc), the stator continuously energizes the rotor to overcome wind resistance as well as friction in the bearings as the rotor spins at high speed. Typical spindle motor speeds include 10,000 revolutions per minute and beyond.
There are several different modes of acoustic noise generated by the spindle motor, including bearing interaction and the reaction force on the stator. With respect to the bearing, it has been found that conventional ball bearing systems generate vibrations as the ball roll within their respective raceways. Even high quality bearings will have microscopic defects within either the raceways or the balls which generate vibrations. However, this source of vibration can be reduced through the use of hydrodynamic bearings which do not require a physical interaction between a ball and a raceway.
With respect to stator vibrations, the continuous interaction between the stator and the rotor tends to create a torsional resonance in the stator. That is, as the stator applies a force to the rotor to control the rotational speed of the rotor, a counter-force is applied by the rotor to the stator in the opposite direction. This reaction force causes the stator (which is made up of a number of individual stator laminations) to vibrate. Furthermore, stator vibrations may occur as a result of the excitation of the stator mass by the application and removal of commutation pulses used to energize the rotor. Commutation pulses are timed, polarization-selected direct current pulses which are directed to sequentially selected stator windings. The rapid rise and fall times of these pulses act as a striking force and set up sympathetic vibrations in the stator structure.
Vibrations within the stator may create acoustic noise either by direct radiation (i.e., from the spindle motor to the air) or through the transmission of vibrations to the disc drive housing (i.e., from the housing to the air). Indeed, it has been determined that, due to the rigid coupling of the stator to the disc drive base plate, stator vibrations transmitted to the base plate of the disc drive represent a significant source of acoustic noise.
Prior attempts to reduce this source of acoustic noise have centered around damping the vibrations while isolating or uncoupling the stator from the base plate through the use of O-rings. Additionally, an encapsulating material has also been applied to at least a portion of the stator to reduce or eliminate vibratory tones emanating from the stator laminations. Both of these methods are described in U.S. Pat. No. 5,694,268 to Dunfield et al., which patent is assigned to the assignee of the present application. However, these prior art solutions require the use of additional components and processing steps during the assembly of the disc drive. Additionally, the use of elastomeric materials such as O-rings or encapsulating material may lead to undesirable outgassing within the disc drive, and the O-rings themselves may experience undesirable xe2x80x9ccreepxe2x80x9d over time. Thus, there is a need in the art to provide a simplified solution for reducing the acoustic noise generated by a spindle motor.
It is with respect to these and other background considerations, limitations and problems that the present invention has evolved.
The present invention relates to a disc drive having a spindle motor that reduces the idle acoustic noise generated by the disc drive by reducing the transmission of vibrations from a stator of the spindle motor to a base plate of the disc drive.
In accordance with one embodiment of the present invention, a disc drive spindle motor includes a rotating hub for supporting one or more storage discs of the disc drive. The rotating hub includes a magnet which together act as a rotor for the spindle motor. The spindle motor also includes a stator having a plurality of windings for generating an electromagnetic force to drive the rotor. The stator defines a first cylindrical surface for contacting a second cylindrical surface of a motor mount. The motor mount may either be attached to a base plate of the disc drive or it may be formed integrally with the base plate of the drive. The second cylindrical surface of the motor mount only contacts a portion of the first cylindrical surface of the stator so that vibrations carried within a remaining portion of the stator that is not contacted by the motor mount are not transferred to the base plate of the disc drive.
In one embodiment of the invention, the second cylindrical surface of the motor mount engages between 20% and 80% of the surface area of the first cylindrical surface of the stator. In another embodiment of the invention, the range is limited to between 30% and 70%, while a still further preferred embodiment requires the second cylindrical surface of the motor mount to engage approximately 50% of the surface area of the first cylindrical surface of the stator.
The present invention can also be implemented as a disc drive having a base plate, a storage disc, and a spindle motor having a rotating hub that supports the storage disc. The hub includes a magnet that together with the rotating hub forms a rotor for the spindle motor. A stator of the spindle motor generates an electromagnetic force to rotate the rotor. The stator includes a first cylindrical surface having a predetermined surface area. The spindle motor further includes a motor mount having a second cylindrical surface that engages only a portion of the first cylindrical surface of the stator.
The present invention can further be implemented as a disc drive having a spindle motor with a stator and a rotating a hub that supports a storage disc. The disc drive includes means for reducing transmission of vibrations from the stator to a base plate of the disc drive.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.